i need some tips on how to adjsut the valves in my 1979 chevy 350. i jsut put a new cam in and set the timing up and everything but now it starts no problem but there is a backfire on the exhaust stroke and u can hear it loudlt through the exhaust the way i was taught to adjsut valves was with the enging running loosen till they clack then tighten till no clack then a half turn i did this and it solved the problem i revved her up a bit and everything seemed fine i came back two hours later and the pop was back any suggestions?

In The Zone

12-03-2007, 08:42 PM

did u make sure the lifters were saturated with lube during reassembly?
if not that could be your problem....

duff

12-03-2007, 08:45 PM

I always go 1/4 turn not a half might have one a little tight

Bocephus

12-03-2007, 09:04 PM

does anyone use feeler gauges? if so do you guys no the specs?

duff

12-03-2007, 09:06 PM

there isnt saposto be a gap on a small block chevy with hydolic lifters so a feeler gaug wont to you any good

Bocephus

12-03-2007, 09:21 PM

but if i already adjusted them any reason as to why they would come unadjusted again or why its popping?

kootenaycat

12-03-2007, 09:58 PM

I would check to see if a rocker stud is pulling out of the head, or a more likely cause would be a worn rocker nut. They are a lock nut, and do wear out. Invest in some locking rocker nuts with the locking screw in the middle.

nbrowser

12-03-2007, 10:24 PM

hrm usual adjustment on a Chev engine is usually, not running, turn the crank by hand until the llifters or rods bottom out, then tighten up the rocker until all movement stops up and down (you shake the pushrod up and down with a couple of fingers) then preload it with an extra 1/4 turn or so and lock it down. Having the intake off is a big help with this if it's already off....

duff

12-03-2007, 11:33 PM

but if i already adjusted them any reason as to why they would come unadjusted again or why its popping?

as the lifters pump up, the space between the lifter and the rocker is gona tighten up, if its popping out the egsaust, start with re adjusting the valves, do it with the engin off, start with #1 at tdc, adjust the valves till the lash is just gone then go 1/4 turn, then move on to #8 I beleve? and folow your firing order, watch the intake valve on the next cylinder, when it closes you know your on the comprestion stroke , I ushually go untill the valve rocker stops moving then just a slight turn of the crank more, go thrugh the whole firing order and re-do you adjustments, if its still poping I would look into something other than you valve adjustmen, cam timming? but it sounda like you just have a tight valve

MUD CHILD

12-04-2007, 12:24 AM

After you got the engine running did you "break" the cam in by turning your idle up to 2500 and let it run for half an hour? A fool proof way when adjusting valves is turn the engine over by hand and when the intake valve is closing you set the exhaust valve on the same cylinder, turn it over again and when the exhaust valve is opening you set the intake, that way you are on the base of the lobe on the cam

automan

12-04-2007, 07:49 AM

what cam did you add?
did you change valve springs?
weak valve springs may cause that too

pumpkin

12-04-2007, 02:10 PM

If you didn't break the cam in properly it can wipe the lobes off a cam in a couple of minutes. The other problem you will run into is that the oil cumpanies have taken the zinc out of the oil. With this gone cam lubrication suffers a hole bunch. This is one of the reasons new vehicles are roller, lifters, rockers, followers. Apparantly shell rottela diesel oil still has zink and they say is about the only oil left for flat tappet cams.

Toyquad

12-04-2007, 02:30 PM

If you didn't break the cam in properly it can wipe the lobes off a cam in a couple of minutes. The other problem you will run into is that the oil cumpanies have taken the zinc out of the oil. With this gone cam lubrication suffers a hole bunch. This is one of the reasons new vehicles are roller, lifters, rockers, followers. Apparantly shell rottela diesel oil still has zink and they say is about the only oil left for flat tappet cams.

thats some good info to know

Troy

12-04-2007, 03:41 PM

the cam had already been in the truck since he got it so its not a break in issue.

78bronco

12-04-2007, 04:08 PM

you might hav a sticky valve

Bocephus

12-04-2007, 08:41 PM

i figured it out im probably the most embarrased i have ever been. i accedentily mixed up the 1 and 3 spark plug trying to get my truck out of the shop sunday night runs like a champ now[16]

duff

12-04-2007, 08:43 PM

at least it was cheap

Bocephus

12-04-2007, 09:00 PM

lol ya but frustrating and annoying

SuperIanMechanic

01-01-2008, 10:02 PM

your ignition timing or timing chain could be causing ya the grief , timing to far advanced or a loose chain but i agree sounds like a lifter is too tight

tchevy

01-07-2008, 07:16 PM

ac delco lifter additive still has zinc, i think gm crate engines even come with it for break in.

FZJ80

01-07-2008, 08:27 PM

GM still sells an engine oil supplement that is great for cam run in. It still has all the good shit in it that is nasty for the enviroment but makes for a proper breakin, but as with anything that works good it is soon to be disscontiued.
Get some while you can!